1. Field of the Invention
The invention relates generally to dispersions of olefins.
2. Background
Aqueous dispersions of a thermoplastic resin of various types are known in the art and have been used in a wide variety of fields. For example, when an aqueous dispersion is coated and dried on a surface of a substrate such as paper, fiber, wood, metal, or plastic molded article, the resin coating formed will provide the substrate with water resistance, oil resistance, chemical resistance, corrosion resistance and heat sealability. An aqueous medium is advantageous compared to an organic dispersion medium in view of common hazards such as flammability, working environment, handling convenience, and the like.
Conventional aqueous dispersions of a thermoplastic resin have been produced either by a process wherein a polymerizable monomer which is the resin raw material is polymerized by emulsion polymerization in an aqueous medium in the presence of a dispersing agent, or by a process wherein a molten thermoplastic resin and an aqueous medium, and optionally a dispersing agent are mixed by applying shearing force.
Until the advent of polyolefin dispersions, polyolefins were typically limited to extrusion and coextrusion processes and thus polyolefins could not be used in coating processes such as paper coating, fabric coating, and the like, nor in very thin layers, e.g., less than 15 microns.
Newer polyolefin dispersions have provided improved performance, but the useful polyolefin dispersions have been limited to those with lower crystallinities, such as ethylene and propylene elastomers and plastomers. Exemplary aqueous dispersions of this sort are disclosed in U.S. Patent Application Publication No. 2005/0100754, which is assigned to the assignee of the present invention. Alternatively, higher crystallinity polyolefins have been dispersed in water, but have required the presence of solvents.
Accordingly, there exists a need for dispersions and foams formed from higher crystallinity thermoplastic polymers, especially olefin-based polymers, where the dispersions are preferably formed without the use of solvents.